1. Field of the Invention
The present invention relates to a circuit for determining positions of contacts on a capacitive position sensing panel, and more particularly, to a circuit using self capacitance and mutual capacitance sensing methods to determine positions of contacts on a capacitive position sensing panel.
2. Description of the Prior Art
Regarding operations of human-machine interface (HMI), position sensing is a widely used function which can be categorized into one of a resistive sensing method, an optical sensing method, an acoustic sensing method, a capacitive sensing method, etc. Due to the fact that the capacitive position sensor does not require stress-strain deformation, has a higher immunity against ambient light and the temperature, and employs a less complex manufacture process, the capacitive position sensing technique is therefore considered to be the most practical one to be part of an integrated process.
Sensing methods of a capacitive position sensor can be divided into a self capacitance sensing method and a mutual capacitance sensing method, wherein the self capacitance sensing method possesses ghosting and snap problems when determining positions of contacts. Thus, when the self capacitance sensing method is used to detect more than two contacts, problems such as misjudgment and indefinite position determination will occur. On the other hand, the mutual capacitance sensing method can accurately detect more than two contacts; however, since the mutual capacitance sensing method uses a step-by-step driving method to detect the contacts, it has stricter requirements on the sensing resolution and operation speed.